This master thesis deals with the cyclic fatigue behaviour of hard metals. The crack growth behaviour of intrinsic defects and artificially introduced long cracks in five different hard metal qualities (variation of grain size and cobalt content) was investigated by different methods. The load situation applied in the tests mirrored the stress state on end mills or end milling cutters during operation close to the chuck or the clamping during the cutting process. All tests were carried out under alternating load, i.e. at a stress ratio of R=-1, using a 6- or 8-point bending device. The distribution of the numbers of cycles to failure at constant load amplitude was determined with approximately 30 specimens per material variant. These data were evaluated using statistical methods so that the parameters of Paris laws for the cyclic crack growth of intrinsic defects could be determined. Crack propagation experiments were carried out with long surface cracks. In these tests, the growth of a single artificially introduced crack was observed until fracture. A da/dN curve with the results from both test types was plotted for each specimen type. The slopes of these crack growth curves and thus the Paris exponents tend to be lower for long cracks than for intrinsic defects. The Paris exponents of the da/dN curves for intrinsic defects lie between n = 27 and n = 55. Due to the large variation of the results, no clear correlation could be established between the Paris exponent and the material parameters grain size or cobalt content. However, it was found that intrinsic defects also grow below the threshold for crack growth observed with long cracks.